Correlation of Urinary Foam with Proteinuria in Patients with Chronic Kidney Disease

Background: Foamy urine is often reported to be associated with proteinuria and kidney diseases. There is no objective measure on the nature and correlation of this relationship. Literature reviews revealed very few studies that can confirm or refute this relationship. This study hypothesized that the severity and persistence of urinary foam were associated with the degree of proteinuria (as determined by urine protein-creatinine ratio and dipstick). Methods: We analyzed urine samples of patients from our chronic kidney disease (CKD) clinics for urine protein and foam. The urine samples were shaken in a standardized way and heights of resting foam (in millimeters) were measured after a pre-determined resting time. The foam heights were correlated with clinical variables including proteinuria, stages of CKD, gender, age, co-morbidities and urine specific gravity. Results: A total of 160 urine samples were analyzed. Greater foam height was significantly associated with advanced CKD stages (p=0.015), urine dipstick protein (p<0.001), urine PCR (p=0.005) and diabetes mellitus (p=0.013). Urine specific gravity (p=0.053) and hypertension (p=0.91) did not achieve statistically significant results with foam height. Further analyses were performed on 54 urine samples with no or low protein level (defined as urine PCR of less than <100 mg/mmol AND urine protein dipstick result of ≤ 1+). In these samples, there was no statistically significant relationship between foam height and CKD stages (p=0.403), specific gravity (p=0.564), diabetes mellitus (p=0.909) and hypertension (p=0.08). Conclusion: Our study showed that urinary foam can be used as a rudimentary surrogate marker for proteinuria in patients with CKD. It provides extra leverage to the age-long assumptions that urinary foam is associated with kidney disease and proteinuria. More research will be needed to ascertain and investigate the nature of this relationship.